Under Flat is the shortest of the flat-tipped attack bits, sitting roughly two millimetres below the standard height that Flat occupies. The tip itself is a broad plastic disc much like Flat’s, so the movement pattern is familiar — it refuses to settle, tracks out to the stadium wall and rides it — but dropping the whole combination closer to the floor changes what that aggression accomplishes. Where Flat trades blows at the opponent’s blade and Low Flat shaves a millimetre for speed, Under Flat comes in beneath the opponent entirely, angling contact upward into the ratchet region. That upward line of attack is why it reads as a burst tool as much as a knockout tool.
Reference rankings put it below Flat, generally alongside Low Flat rather than above it. The reason is control: Under Flat gives you very little of it, and its stamina is poor even by attack-bit standards, so a battle that goes long is a battle already lost. It is a bit for players who intend to end things in the opening seconds and accept the risk of self-knockout when they don’t.
Build around it with high-recoil attack blades and short ratchets — the low profile only pays off if nothing above it adds height back. Players who find it too volatile move to Flat for the extra stamina and margin for error. One practical warning that is well documented: repeated contact with the X-Celerator rail chews this bit up unusually fast, and anyone using it seriously is expected to own spares.